Telecommunications networks transport signals between user equipment at diverse locations. A telecommunications network includes a number of components. For example, a telecommunications network typically includes a number of switching elements that provide selective routing of signals between network elements. Additionally, telecommunications networks include communication media, e.g., twisted pair, fiber optic cable, coaxial cable or the like that transport the signals between switches. Further, some telecommunications networks include access networks.
For purposes of this specification, the term “access network” means a portion of a telecommunication network, e.g., the public switched telephone network (PSTN), that allows subscriber equipment or devices to connect to a core network. For purposes of this specification, the term access network further includes customer located equipment (CLE) even if commonly considered part of an enterprise network. Examples of conventional access networks include a cable plant and equipment normally located in a central office or outside plant cabinets that directly provides service interface to subscribers in a service area. The access network provides the interface between the subscriber service end points and the communication network that provides the given service. An access network typically includes a number of network elements.
A network element is a facility or the equipment in the access-network that provides the service interfaces for the provisioned telecommunication services. A network element may be a stand-alone device or may be distributed among a number of devices. A network element is either central office located, outside plant located, or customer located equipment (CLE). Some network elements are hardened for outside plant environments. In some access networks as defined herein, various network elements may be owned by different entities. For example, the majority of the network elements in an access network may be owned by one of the Regional Bell Operating Companies (RBOCs) whereas the CLE may be owned by the subscriber. Such subscriber equipment is conventionally considered part of the subscriber's enterprise network, but, for purposes of this specification may be defined to part of the access network.
There are a number of conventional forms for access networks. For example, the digital loop carrier is an early form of access network. The conventional digital loop carrier transported signals to and from subscriber equipment using two network elements. At the core network side, a central office terminal is provided. The central office terminal is connected to the remote terminal over a high-speed digital link, e.g., a number of T1 lines or other appropriate high-speed digital transport medium. The remote terminal of the digital loop carrier typically connects to the subscriber over a conventional twisted pair drop.
The remote terminal of a digital loop carrier is often deployed deep in the customer service area. The remote terminal typically has line cards and other electronic circuits that need power to operate properly. In some applications, the remote terminal is powered locally. Unfortunately, to prevent failure of the remote terminal due to loss of local power, a local battery plant is typically used. This adds to the cost and complicates the maintainability of the remote terminal, due to the outside plant operational requirements which stipulate operation over extended temperature ranges.
In some networks, the remote terminal is fed power over a line from the central office. This is referred to as line feeding or line powering and can be accomplished through use of an AC or a DC source. Thus, if local power fails, the remote terminal still functions because it is typically powered over the line using a battery-backed power source. This allows the remote terminal to offer critical functions like lifeline plain old-fashioned telephone service (POTS) even during a power outage.
In a typical system offering line powering, the circuit that injects the power also is the source of the communication signals provided to the communication lines. The design of the power injection circuitry becomes complicated when the power signal is inserted in a different circuit from the circuit that terminates the communication signals. Therefore, there is a need in the art for improvements in the manner in which power is provided to network elements in an access network to allow injection of power signals onto a line carrying communication signals.